1. Field of the Invention
The present invention relates to a chemical air filtering device comprising an active filter section in series with a conventional and universal filter section. The active filter section comprises a reagent capable to capture a target toxic pollutant having a chemically active function and to derive it into inert, non volatile and non-toxic matter. The main filter section is positioned downstream the active filter section to capture other types of pollutants passing through the active section.
2. Brief description of the prior art
The conventional respiratory masks using a chemical cartridge are not safe enough against toxic pollutants having a chemically active function such as for example the isocyanates. The isocyanates mixed with other solvents are found in the paint shops, polyurethane foam factories, foundries, chemical plants, etc., and, as the workers are exposed, they can cause very serious respiratory illnesses such as acute poisoning, acute and chronic respiratory functional affections, professional asthma, etc. even at very low concentrations.
Masks supplied with fresh air efficiently protect the workers against the isocyanates and other toxic pollutants. However, in many instances it is, if not impossible, practically very difficult to use such masks. It is the case for example when the working area is exiguous, when the access to the working area is difficult, or when accumulations of aerosol on the visor of the mask cause visual problems. Also use of these masks is expensive.
In these environments, the workers often wear protective respiratory masks with a conventional chemical cartridge which generally lacks efficiency and safety against the toxic pollutants. The workers can therefore be exposed at least to small concentrations of toxic pollutant. Need has accordingly arisen for an efficient and safe alternative to the conventional chemical cartridges available on the market.
To that effect, the publication "PROTECTION OF THE RESPIRATORY ORGANS AND SKIN OF DIISOCYANATE WORKERS" by 0. K. Ardasheva, V. I. Astrakhantseva and V.I. Tsivtsina, INSTITUTE OF INDUSTRIAL HYGIENE AND OCCUPATIONAL DISEASES, Gor'kiy pp. 92-95, 1964, suggests a protective respiratory cartridge comprising a layer of activated carbon and a layer of absorbent B in the ratio 1:4.5. The activated carbon is placed upstream the absorbent B which is therefore the layer closest to the user. This cartridge was tested with diisocyanates as the target pollutants. As the absorbent B is not capable of deriving the diisocyanates into inert, non volatile and non toxic matter, the pollutant can migrate through the absorbent and can therefore be inhaled by the user. The pollutant also migrates when the mask is unused and can of course be inhaled when the mask is subsequently worn.
Regarding U.S. Pat. No. 4,643,182 (Klein) issued on Feb. 17, 1987, it proposes a protective respiratory mask using activated carbon to capture pollutants present in the inhaled air. The activated carbon itself contains a chemical substance capable of deriving a target toxic pollutant into inert matter. The chemical substance removes from the air the toxic pollutant while the activated carbon captures the other types of pollutants. A drawback of the mask of Klein is that the volume of the mask comprises regions with a lower concentration of chemical substance which allow passage of toxic pollutant. Also toxic pollutant captured in the activated carbon migrates through the mask when the same is unused. The so captured toxic matter can of course be inhaled when the mask is subsequently worn.